Significance of the Level of CD20 Expression Determined by Mean Fluorescence Intensity Ratio Using Flow Cytometry in Diffuse Large B-Cell Lymphoma
M Shahjahan, NJ Nelles, Y Feng, Y Zu, A Ewton, CC Chang. The Methodist Hospital, Houston, TX
Background: Diffuse large B cell lymphoma (DLBCL) accounts for more than 40% of non-Hodgkin lymphomas. CD20 is a B cell specific marker that shows marked variability in its expression among and within different lymphoma subtypes. A recent study reported that reduced CD20 expression by neoplastic B cells, as measured by mean fluorescence intensity (MFI) by flow cytometry (FCM), is associated with inferior overall survival (OS) in DLBCL patients. The goal of this study was to use a more quantitative method to determine the MFI ratio of neoplastic CD20 positive B cells to non-neoplastic B cells to further study its clinical significance.
Design: Fifty three cases with pathologically confirmed diagnosis of DLBCL who had FCM analysis performed between 2003 & 2008 were included in this study. There were 32 males and 21 females with median age of 69 years. MFI of CD20 expression in clonal and normal B cells and MFI of CD71 expression in B cells were determined by FCM. All patients received cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) or CHOP like regimen with Rituximab. Clinical follow-up data was gathered from the Cancer Registry of The Methodist Hospital.
Results: There was no statistically significant impact on OS by stratifying the cases with MFI ratio < 2 (neoplastic B lymphocytes expressing lower level of CD20 than the normal B cells) versus cases with MFI ratio >2 (p=0.44, Kaplan-Meier). Of particular interest, cases with MFI ratio of >3.5 (neoplastic B cells expressing >3.5 times of CD20 than normal B cells) showed much shorter survival compared to cases with MFI ratio <1 (median survival 14 months vs. 29 months, p =0.04, t-test). Additionally, our results showed that cases with a lower MFI of CD71 expression had higher neoplastic to normal B cell mean MFI ratio (p=0.04, t-test).
Conclusions: Our results indicate an inverse correlation between MFI ratio and CD71 expression of neoplastic B cells suggesting that the CD71 bright B cells with a higher proliferation potential may have weaker CD20 expression. However, there is no correlation between OS and the MFI ratio in this cohort. Furthermore, our data also emphasize that higher CD20 expression does not always predict a superior survival in DLBCL patients. No specific cut-off value for MFI that may actually predict survival in DLBCL has been reported in the literature. Therefore, further studies with larger cohort of patients are needed to determine its clinical significance.
Wednesday, March 24, 2010 9:30 AM
Poster Session V # 182, Wednesday Morning